1. Field of the Invention
The invention is related to electronic fuel injection systems for internal combustion engines and in particular to a circuit for generating a fuel enrichment signal increasing fuel delivery to the engine during a start attempt.
2. Description of the Prior Art
It is well known by those skilled in the art that the air/fuel mixture supplied to an internal combustion engine during a start attempt and for a short period of time immediately following a successful start should be enriched to facilitate starting the engine and to sustain the operation of the engine after it has been started. This enrichment is in addition to the conventional warm-up enrichment. A hot engine as used herein designates an engine whose temperature is higher than the normal operating temperature. The hot engine condition normally referred to as a "hot soak" occurs for a period of time after the engine has been stopped after sustained operation. During the period when the engine is hot, fuel in the fuel injectors and fuel lines supplying fuel to the injectors experiences a similar increase in temperature and decreases the density of the fuel. Therefore, the quantity of fuel being injected into the engine is less than the quantity required to sustain operation. The problem becomes even more aggrevated when the temperature is sufficient to cause partial vaporization of the fuel thereby reducing the delivered quantity of fuel even further. Fortunately, this problem only exists for a short period of time after the engine has been started. As the hot fuel is delivered to the engine, it is replaced with fuel at ambient temperature and the fuel delivery soon returns to normal.
The need for temporarily enriching the air/fuel mixture to the engine during a start attempt and for a short period of time immediately following a cold start is eminently more well known and provisions for enriching the air/fuel mixture following starts are presently part of most fuel control systems, both mechanical as well as electronic.